The present invention generally relates to a color image reading apparatus so arranged that, by projecting light onto an original document, reflected light from the surface of the original document is subjected to color separation by filters in a plurality of colors. It is subsequently photo-electrically converted by a solid state image pick-up element or the like, and more particularly, to a change-over mechanism for filters in a plurality of colors for use in such color image reading apparatus.
Conventionally, as disclosed, for example, in Japanese Patent Laid-Open Publication No. 58-43658, there existed an image reading apparatus of a stationary original document type in which an image reading optical system is formed in a unit for scanning. The device scanned over the surface of an original document in a manner that, not only a sheet-like original document, but a book-type original document (e.g. a book) could be read as well.
Meanwhile, with regard to a color image reading apparatus for reading an original document in color, there has conventionally existed an arrangement in which light projected onto, and reflected from, an original document was subjected to color separation by displacing filters. The filters were displaced in a plurality of colors vertically, laterally, or through rotation as disclosed, for example, in Japanese Patent Laid-Open Publication No. 60-206361 or No. 61-84150.
However, in the prior art techniques as referred to above, a complicated change-over mechanism was required in addition to a requirement for an exclusive driving source the filter change-over mechanism in order to efficiently change over the filters of a plurality of colors. Further, for example, when such a filter change-over mechanism is incorporated into the image reading apparatus of the stationary original document type as previously referred to, special mechanisms for supporting the image reading unit and a large driving source for the driving the filter change-over mechanism. Thus, thereof are required the image reading unit becomes larger in size and heavier in weight.